Many energy systems are adversely affected by the need to match a varying power output to a varying load. It is advantageous to be able to store excess energy produced when power output exceeds the demand and subsequently to use this stored energy during periods of peak demand. Flywheels are one method of storing energy. The energy stored in a flywheel is the kinetic energy of the spinning mass of the flywheel. The centripetal forces in a spinning flywheel induce radial and tangential stresses in the body of the fly-wheel. As the angular velocity of the flywheel increases, the stored energy and the induced stresses increase. The flywheel will fail when the induced stresses exceed the breaking strength of the flywheel material. Materials with high breaking strengths are therefore desirable for use in the construction of a flywheel. An object of this invention is to provide a method for the use of high strength materials in the construction of a flywheel.
The stresses induced in the body of a flywheel are not necessarily uniformly distributed through the material of the flywheel and the flywheel fails at that point where the stress is greatest even though the rest of the material may be relatively unstressed. Maximum specific energy (stored energy per unit mass) and energy density (stored energy per unit volume) are achieved when the entire body of the flywheel is stressed to its limit. An object of this invention is to provide methods of constructing a flywheel which permit all of the material in the body of the flywheel to be stressed to the limit.
Many high strength materials are in the form of fibers (e.g., fiberglass, carbon filaments). These materials are utilized by bonding together many filaments into a single body. Such materials are anisotropic in that they can sustain high stresses only along the axes of the filaments. In directions perpendicular to the filament axes the sustainable stress is that of the bonding material. To take advantage of such anisotropic materials in the construction of a flywheel it is necessary to control the stress distribution so that the maximum induced stresses are equal to the stress limits of the filaments and are oriented along the axes of the filaments, while stresses perpendicular to the filament axes are reduced to the limits of the bonding material. It is an object of this invention to provide methods of constructing a flywheel from anisotropic materials which provide such a stress distribution pattern.